Inside the firewall, solar particles dominate. Outside, interstellar particles take over. Voyager showed how solar influence diminishes sharply at this edge.
The boundary between solar wind and interstellar space forms a turbulent layer often described as a firewall. It is here that particles, plasma, and magnetic fields shift dramatically.
Voyager 1 crossed this boundary in 2012, followed by Voyager 2 in... [846 chars]